Pattern transfer device and pattern transfer method

ABSTRACT

According to one embodiment, a pattern transfer device includes a substrate, a transfer unit and a controller. The transfer unit is configured to have electrodes and transfer a pattern corresponding to the electrodes with a voltage applied between the substrate and the electrodes. The controller is configured to control humidity between the substrate and the transfer unit.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2016-065741, filed on Mar. 29, 2016; theentire contents of which are incorporated herein by reference.

FIELD

Embodiments relate to a pattern transfer device and a pattern transfermethod.

BACKGROUND

Semiconductor devices have increasing requirements for miniaturizationand reduction in fabrication costs.

One of the promising next-generation lithography technologies isnanoimprint lithography (NIL) that can transfer nanometer-scale patternwith low fabrication costs. In nanoimprint lithography, the size of apattern on a master mold defines the pattern transfer resolution. Totransfer a high-resolution pattern, a mold with a very fine pattern isneeded, thereby increasing the fabrication costs. In addition,uniformity of the residual layer and processing on the residual layerstill need to be considered. To solve the problems above, a novelsidewall nanoelectrode lithography method has been developed. Thismethod is a resist-less method and allows high-resolution patterntransfer that is not restricted to the size of the pattern on the mastermold.

The sidewall nanoelectrode lithography uses nanoelectrodes formed onsidewalls of an insulating pattern on an insulating mold, and causesvoltage and current to be applied between the sidewall nanoelectrodesand a transfer substrate to electrically transfer a patterncorresponding to the form of the sidewall nanoelectrodes onto asubstrate. Sidewall nanoelectrodes having a thickness of a fewnanometers can, in principle, transfer a nanometer-scale pattern as awhole corresponding to the size of the sidewall nanoelectrodes. Unlikethe conventional nanoimprint technology, this method can transfer afiner pattern than the convex pattern formed on the mold. The sidewallnanoelectrode lithography is also advantageous over a probe lithographyin that it can achieve higher throughput. The sidewall nanoelectrodelithography is a resist-less method and thus can avoid problems relatingto, for example, the residual layer in nanoimprint lithography.

A transferred pattern fabricated by this method normally has a thicknessof about sub-nanometer to 10 nm. Such a transferred pattern, when usedas an etch mask, fails to satisfy a thickness requirement of severaltens of nanometers or more in the etch process. When the transferredpattern is used as an etch mask in fabricating a multi-purpose finepattern, the transferred pattern is preferably a thicker pattern with athinner linewidth. In other words, a transferred pattern with a highaspect ratio is desired. However, due to some environmental factors suchas humidity and temperature in a pattern transfer process, a thickcontiguous water film is formed over the surface of the substrate and alarge meniscus is formed at a transfer unit, which preventshigh-resolution pattern transfer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a pattern transfer device fornanoimprint lithography including sidewall electrodes;

FIGS. 2A and 2B are diagrams each illustrating an example of howhumidity affects the meniscus formed at a transfer unit in transferringa pattern;

FIG. 3 is a graph illustrating the relation between the humidity of atransfer atmosphere and the thickness of a water film formed on asilicon (Si) transfer substrate;

FIG. 4 is a diagram illustrating a pattern transfer device according toa first embodiment;

FIG. 5 is a diagram illustrating a structure of a transfer unit;

FIG. 6 is a diagram illustrating an example of an alternating current(AC) bias voltage to be applied between the transfer unit and a transfersubstrate;

FIGS. 7A to 7F are scanning electron microscope (SEM) picturesillustrating results of pattern transfer under humidity conditionsranging from 40 to 80%;

FIG. 8 is a diagram illustrating a pattern transfer device according toa first modification of the first embodiment;

FIG. 9 is a diagram illustrating a pattern transfer device according toa second modification of the first embodiment;

FIG. 10 is a diagram illustrating a pattern transfer device according toa second embodiment;

FIG. 11 is a diagram illustrating a pattern transfer device according toa first modification of the second embodiment;

FIG. 12 is a diagram illustrating a pattern transfer device according toa second modification of the second embodiment; and

FIG. 13 is a diagram illustrating a pattern transfer device according toa third modification of the second embodiment.

DETAILED DESCRIPTION

The following describes a pattern transfer device and a pattern transfermethod according to embodiments with reference to the accompanyingdrawings.

According to one embodiment, the pattern transfer device includes asubstrate, a transfer unit and a controller. The transfer unit isconfigured to have electrodes and transfer a pattern corresponding tothe electrodes with a voltage applied between the substrate and theelectrodes. The controller is configured to control humidity between thesubstrate and the transfer unit.

A typical scanning probe microscope (SPM) lithography that uses aconductive probe can fabricate a high-resolution pattern but with a verylow throughput. In recent years, the semiconductor industry has focusedon nanoimprint lithography (NIL) as a low-cost lithography technologythat can transfer a fine pattern as a whole. In nanoimprint lithography,however, the resolution of the pattern on the master mold defines theresolution of the transferred pattern. To fabricate a high-resolutionpattern in nanoimprint lithography, a mold with a very fine pattern isneeded, which causes an increase in master cost. In nanoimprintlithography, uniformity of the residual layer and processing on theresidual layer still need to be considered. The following describes anexample of a technology that is a resist-less technology and cantransfer a pattern at higher resolution irrespective of the size of apattern on a mold.

As a technology that can achieve a higher resolution than the size ofthe pattern on the mold, an imprint technology (hereinafter referred toas a sidewall electrode lithography) is known. The sidewall electrodelithography uses a mold (hereinafter referred to as a sidewall electrodemold) including sidewall electrodes for pattern transfer on the sidesurfaces of protruding structures.

FIG. 1 illustrates an example of a pattern transfer device including asidewall electrode mold. In nanoimprint lithography, this patterntransfer device 10 includes a mold 11 having sidewall electrodes 12, atransfer substrate 13, and a power source 15. The sidewall electrodes 12on the mold 11 are pushed to the transfer substrate 13 and a voltage isapplied between the transfer substrate 13 and the sidewall electrodes12. With this process, a pattern 14 corresponding to the sidewallelectrodes 12 can be formed on the transfer substrate 13.

The sidewall electrode lithography is an imprint technology that uses asidewall electrode mold instead of using a conductive probe. Thesidewall electrode lithography can transfer a pattern corresponding tothe sidewall electrodes as a whole onto a transferee target by anelectrochemical reaction. The sidewall electrode lithography includes acontact method and a contact-less method. In a contact sidewallelectrode lithography, the sidewall electrode mold is brought intocontact with a target substrate (hereinafter referred to as a transfersubstrate) and the pattern formed by the sidewall electrodes istransferred to the transfer substrate. In a contact-less sidewallelectrode lithography, portions that form a pattern are kept near thetransfer substrate and the pattern is transferred to the transfersubstrate. The following mainly describes the contact sidewall electrodelithography, but the following embodiments are also applicable to thecontact-less sidewall electrode lithography.

In the contact sidewall electrode lithography, the contact state betweenthe portions that form a pattern and the transfer substrate may largelyaffect the transfer characteristic. To uniformly transfer a pattern tothe transfer substrate, it is especially important for the sidewallelectrodes to be uniformly in contact with the transfer substrate. Inthe contact-less sidewall electrode lithography, it is especiallyimportant to keep a constant space between each sidewall electrode andthe transfer substrate to uniformly transfer a pattern.

In the sidewall electrode lithography, proper control on the humidity ofthe atmosphere is desired in transferring a pattern to improve theuniformity of the transferred pattern. In terms of material costs andmaterial fabricability, using a mold made of silicon is effective.However, silicon is oxidized by oxygen in the atmosphere. This oxidationforms natural oxides such as SiO_(x) that are hydrophilic. Thus, whenthe mold is made of silicon, ends of the protruding portions of the moldthat are in contact with or near the transfer surface are hydrophilic.Using a mold having hydrophilic portions that are in contact with ornear the transfer substrate forms a larger meniscus at each electrode.This situation may reduce the transfer resolution.

FIGS. 2A and 2B are diagrams each illustrating an example of an effectof the humidity in transferring a pattern with the sidewall electrodemold being pushed onto the transfer substrate. FIG. 2A illustrates acase when humidity between the transfer substrate and the sidewallelectrode mold is 40%, and FIG. 2B illustrates a case when humiditybetween the transfer substrate 13 and the sidewall electrode mold 11 is80%. When the humidity is 80%, a thick water film 18 is formed on thetransfer substrate 13 and a larger meniscus 16 is formed at eachelectrode 12. In this situation, a larger transfer oxide 17 is formedand the transfer resolution is reduced compared to the case of humidityof 40%.

FIG. 3 is a graph illustrating the relation between the humidity betweenthe transfer substrate and the sidewall electrode mold and the thicknessof the water film formed on the transfer substrate. The thickness of thewater film rapidly increases at humidity of 80% or more. However, thehumidity of 30% or lower fails to provide enough water to form apattern, which results in an insufficient pattern formation. To transfera pattern at a high resolution, the humidity on the transfer substrateneeds to be controlled to 30% or more and 80% or less.

Moreover, the inventors have found that controlling the voltage to beapplied between the transfer substrate and the sidewall electrode moldcan form a pattern with high aspect ratio.

The following embodiments describe a pattern transfer device and apattern transfer method that can prevent a wider linewidth of a patterncaused by the water film on the substrate at a high humidity and canimprove the aspect ratio by optimization of transfer voltage conditions.

The same reference signs indicate the same constituent parts. Thedrawings are schematic and conceptual ones and thus the relation betweenthe thickness and width and the dimensional ratio between parts in thedrawings are not necessarily the same as those in the actual device. Thesame part may be illustrated in a different dimension or a ratiodepending on the drawings.

First Embodiment

FIG. 4 is a diagram illustrating a pattern transfer device according toa first embodiment.

This pattern transfer device 1 includes a transfer unit 2 and a transferunit holder 6 at the transferring side, and a transfer substrate 3, ahumidity controller 4, and a transfer substrate holder 7 at thetransferee side, and includes a power source 5.

The transfer unit 2 at the transferring side is attached to the transferunit holder 6. The transfer unit holder 6 has, for example, a pluralityof suction openings 6 a through which the transfer unit 2 is drawn to beheld by the transfer unit holder 6. The transfer unit 2 is notnecessarily held by suction. The transfer unit 2 may be held by anymethod that can stably hold the transfer unit 2, such as using magnets,a sandwiching tool, or clips. The transfer unit 2 is the aforementionedsidewall electrode mold.

On the transfer substrate holder 7 at the transferee side, the humiditycontroller 4 is provided that controls humidity. The transfer substrate3, on which a pattern will be transferred, is placed on the humiditycontroller 4 with a surface (pattern transfer surface) on which thepattern will be transferred facing upwards. The transfer substrateholder 7 has, for example, a plurality of suction openings 7 a throughwhich the humidity controller 4 is drawn to be fixed on the transfersubstrate holder 7. The humidity controller 4 has openings 4 a that arein communication with at least one of the openings 7 a of the transfersubstrate holder 7. With this configuration, the transfer substrate 3 isfixed onto the humidity controller 4 by suction through the openings 7 aof the transfer substrate holder 7. The transfer substrate 3 is thusfixed to the transfer substrate holder 7. The transfer substrate 3 isnot necessarily held by suction. The transfer substrate 3 may be held byany method that can stably hold the transfer substrate 3, such as usingmagnets, a sandwiching tool, or clips.

The transfer unit 2 includes a base 2 a, a plurality of protrudingstructures 2 b, and an extraction electrode 2 c connecting to theprotruding structures 2 b. The transfer unit 2 is held by the transferunit holder 6 such that a surface 2 d of each protruding structure 2 bfaces the pattern transfer surface of the transfer substrate 3. At leastone of the transfer unit holder 6 and the transfer substrate holder 7 ismovable in the Z direction by a moving mechanism (not illustrated).

In the first embodiment, the power source 5 is an AC power source. An ACvoltage is applied between the extraction electrode 2 c of the transferunit 2 and the transfer substrate 3 in transferring a pattern.

FIG. 5 is a diagram illustrating an example of a contact sidewallelectrode mold. The transfer unit 2 includes the base 2 a, theprotruding structures 2 b and the extraction electrode 2 c. The base 2 ais a base member of the transfer unit 2. The base 2 a may be made of aninsulating material such as silicon or quartz. The base 2 a may be madeof an insulating resin such as polydimethylsiloxane (PDMS) orparaxylene. The base 2 a may be made of an insulating material havingoptical transparency.

The protruding structures 2 b each have a mesa structure provided on afirst main surface 2 e of the base 2 a. In FIG. 5, the protrudingstructures 2 b extend in the Y direction on the first main surface 2 eof the base 2 a and are arranged at certain intervals in the Xdirection. However, the arrangement of the structures is not limited tothis. The arrangement may be modified in various other forms inaccordance with the layout of the pattern to be transferred. Thetransfer unit 2 may have another structure in which gaps betweenadjacent protruding structures 2 b are filled with, for example, ahydrophobic insulating material to make the gaps flush with theprotruding structures 2 b.

The protruding structures 2 b each have a protruding portion 2 f, afunctional layer 2 g, and one or more sidewall electrodes 2 h. Theprotruding portion 2 f has a mesa structure protruding from the firstmain surface 2 e of the base 2 a, and is made of an insulating materialsuch as silicon, quartz, or a resin. The protruding portion 2 f nay be amachined structure cut out from a bulk base material (for example, asubstrate) from which the base 2 a is formed, or a joined structureattached to the base 2 a. The protruding portion 2 f may have a taperedshape to, for example, facilitate fabrication of the protruding portion2 f in a fabrication process.

The functional layer 2 g covers at least the top end of the protrudingportion 2 f in the Z direction. The functional layer 2 g has noelectrode function, but has a function of providing uniform contactbetween the sidewall electrodes 2 h and the target transfer substrate 3.Thus, the functional layer 2 g is made of an insulating material that ismore deformable than the protruding portion 2 f (or the base 2 a). Forexample, the functional layer 2 g is made of an insulating materialhaving a Young's modulus of a few to several tens of percent relative tothe Young's modulus of the protruding portion 2 f.

In the contact sidewall electrode lithography, the functional layer 2 gis brought into contact with the transfer substrate 3. Thus, thefunctional layer 2 g can have a thickness ranging from a few nanometers(nm) to a few micrometers (μm). In terms of overall contact with thetransfer substrate 3 and deformability of the functional layer 2 g, thethickness of the functional layer 2 g is preferably 10 nm or more and 10μm or less.

The functional layer 2 g is preferably made of a hydrophobic material toprevent a large meniscus from forming with the water in the atmospherein transferring a pattern. For example, the functional layer 2 g ispreferably made of a hydrophobic material that has a water contact angleof 45° or more. Examples of the material that satisfies such arequirement include CYTOP (registered trademark), hexamethyldisilazane(HMDS), polymethyl methacrylate (PMMA), polytetrafluoroethylene (PTFE),and Teflon (registered trademark) AF. In terms of ease of processing,using polymethyl methacrylate (PMMA) is preferable. The material of thefunctional layer 2 g is not limited to these materials. The material maybe any insulating material that is softer than the material of theprotruding portion 2 f and has a higher hydrophobicity than the oxidesof the material of the protruding portion 2 f.

The functional layer 2 g is not limited to a single layer structure, butmay have a multi-layer structure.

Although the functional layer 2 g is described in this context, thefunctional layer 2 g is not a necessary element to implement the firstembodiment. Thus, the first embodiment includes absence of thefunctional layer 2 g.

The sidewall electrodes 2 h are structures for transferring a pattern tothe transfer substrate 3. End portions (hereinafter referred to as endsurfaces) of the sidewall electrodes 2 h adjacent to side surfaces ofthe functional layer 2 g defines the form of the transferred pattern.The sidewall electrodes 2 h are made of a conductive material such as aconductive metal or a conductive metal oxide. Examples of the conductivematerial include Ru, Pt, Rh, W, Ni, Au, Ir, RuO, and IrO_(x), but theconductive material is not limited to these.

The sidewall electrodes 2 h are each provided on a side surface of thefunctional layer 2 g to a side surface of the protruding portion 2 f. Inother words, the sidewall electrodes 2 h are each provided on a sidesurface of a protruding structure composed of the protruding portion 2 fand the functional layer 2 g.

The form of the sidewall electrodes 2 h corresponds to the pattern to betransferred to the transfer substrate as described above. Thus,adjusting the width (corresponding to the thickness of the sidewallelectrodes 2 h) of the end surface of each sidewall electrode 2 h canadjust the width of a pattern to be transferred to the transfersubstrate 3. The width of the end surface of the sidewall electrode 2 hmay be set to a width narrower than, for example, the width of theprotruding portion 2 f or may be set to a fraction to some tenths of thewidth of the end surface of the protruding portion 2 f. For example, thewidth of the end surface of the sidewall electrode 2 h may be set toabout a few nanometers to several hundreds nanometers.

The sidewall electrodes 2 h that form a pattern are preferablypositioned at substantially the same height level in the Z direction asthat of a surface of the functional layer 2 g on the side of thetransfer substrate 3. Considering the deformable characteristic of thefunctional layer 2 g, the sidewall electrodes 2 h may be positioned at aheight level different from the height level of the surface of thefunctional layer 2 g on the side of the transfer substrate 3 within therange of the deformable characteristic of the functional layer 2 g.

The extraction electrode 2 c is formed on, for example, a region that isnot formed with the protruding structures 2 b on the first main surface2 e of the base 2 a to a side surface 2 j or to the back surface (asecond main surface 2 k opposite to the first main surface 2 e) of thebase 2 a. The extraction electrode 2 c is used to electrically draw thesidewall electrodes 2 h. The extraction electrode 2 c connects to anexternal electrode from which current flows in transferring a pattern toform an electrical connection. The extraction electrode 2 c may be madeof a metal such as Al, Cu, W, or Au. The material of the extractionelectrode 2 c is not limited to these, but may be a conductive materialof various other kinds.

The transfer substrate 3 is a semiconductor substrate such as a siliconsubstrate. As described above, the transfer substrate 3 is drawn fromthe openings 7 a of the transfer substrate holder 7 to be fixed onto thehumidity controller 4.

The humidity controller 4 controls the humidity between the transferunit 2 and the transfer substrate 3. Specifically, the humiditycontroller 4 includes a sensor (not illustrated) that measures a firsttemperature and a first humidity of the atmosphere (hereinafter referredto as the atmosphere) between the transfer unit 2 and the transfersubstrate 3, a calculation unit that calculates the dew point of theatmosphere based on the first temperature and the first humiditymeasured by the sensor, and a temperature control unit that controls thetemperature of the transfer substrate 3 to a second temperature based onthe dew point so that the humidity near the surface of the transfersubstrate 3 will be a certain second humidity. The temperature controlunit may be configured by a Peltier device or a heater.

As the atmospheric temperature drops, water vapor contained in theatmosphere forms water droplets, and the dew point is the temperaturebelow which the water droplets begin to condense.

The humidity control method implemented by the humidity controller 4begins with measurement of the first temperature and the first humidityof the atmosphere by the sensor, and then the dew point of theatmosphere is calculated from, for example, a known conversion table.The temperature control unit calculates the second temperature of thetransfer substrate 3 based on the calculated dew point. The secondtemperature is necessary for the second humidity that is the targethumidity. When the second temperature is higher than the firsttemperature, the temperature control unit heats the transfer substrate 3to the second temperature by using, for example, a Peltier device. Whenthe first temperature measured by the sensor comes closer to the targetsecond temperature, the temperature control unit stops heating. When thefirst temperature measured by the sensor drops from the secondtemperature by certain degrees, the temperature control unit may heatthe transfer substrate 3 again to keep the temperature at about thesecond temperature. When the second temperature is lower than the firsttemperature, the temperature control unit cools the transfer substrate 3to the second temperature by using, for example, the Peltier device.

Until dew condensation, moisture content of the atmosphere is unchangedif the temperature changes. At a dew point temperature, humidity of theatmosphere is 100%. Thus, a second temperature T can be calculated basedon the moisture content of the atmosphere at the dew point temperatureand the moisture content of the atmosphere at a second humidity B.

Suppose that the dew point temperature obtained from the firsttemperature and the first humidity is represented by A (° C.), and thesecond humidity that is the target humidity is represented by B (%), thesecond temperature T is obtained in the following manner.

First, a saturated vapor pressure C at the dew point is obtained. Thesaturated vapor pressure C is obtained by the following expression.

$\begin{matrix}{C = {6.11 \times 10^{\frac{7.5 \cdot A}{A + 237.3}}}} & (1)\end{matrix}$

A saturated vapor pressure D at the second temperature T is obtainedfrom the second humidity B and the saturated vapor pressure C at the dewpoint by the following expression.

D=C÷B×100  (2)

The saturated vapor pressure D at the temperature T is also obtained bythe following expression.

$\begin{matrix}{D = {6.11 \times 10^{\frac{7.5 \cdot T}{T + 237.3}}}} & (3)\end{matrix}$

The following expression is obtained by substituting Expression (1) andExpression (3) for Expression (2) and solving for the temperature T.

$\begin{matrix}{{T = \frac{237.3 \times {\log_{10}(E)}}{7.5 - {\log_{10}(E)}}}{E = {10^{({\frac{7.5 \cdot A}{A + 237.3} + 2})}/B}}} & (4)\end{matrix}$

Thus, the second temperature T is obtained by Expression (4).

The second humidity that is the target humidity near the transfersubstrate 3 may be directly input through, for example, a built-in panelprovided to the humidity controller 4, or may be automaticallydetermined by the humidity controller 4 such that the second humidity iskept at, for example, 40% or more and 60% or less. Based on thishumidity, the temperature of the transfer substrate 3 may be controlled.

When, for example, the first temperature and the first humidity of theatmosphere is 25° C. and 80%, respectively, and the second humidity nearthe transfer substrate 3 is 60%, the second temperature of the transfersubstrate 3 is controlled to 29.9° C. For such a dew point andtemperature calculation, using a computer or other computing devices ispreferred. Such a computing device can perform the aforementionedcalculation instantly.

The temperature of the atmosphere and the surface temperature of thetransfer unit 2 and the transfer substrate 3 may be measured by, forexample, a thermography.

According to the results of experiments, controlling the secondtemperature of the transfer substrate 3 by the humidity controller 4 sothat the humidity on the surface of the transfer substrate 3 is kept at30% or more and 80% or less successfully prevented a large meniscus fromforming in transferring a pattern, thereby preventing degradation oftransfer resolution. In particular, when the humidity was kept at 40% ormore and 60% or less, a precisely controlled pattern was successfullyfabricated. When the humidity on the surface exceeded 80%, dew wasformed on the transfer substrate 3 as described above, and a largemeniscus was formed due to an effect of an excessively formed waterfilm, thereby lowering the transfer resolution. When the humidity on thesurface was below 30%, no water film for forming a pattern was formed onthe transfer substrate 3, and no pattern could properly be transferred.The humidity controller 4 may include a power source of its own or maybe connected to another power source (not illustrated) that is differentfrom the power source 5 included in the pattern transfer device 1.

The power source 5 applies voltage between the transfer unit 2 and thetransfer substrate 3. The voltage to be applied is mainly an AC biasvoltage.

A probe anodic oxidation lithography is known that can improve an aspectratio of a fabricated pattern by application of an AC bias voltage.Applying the AC bias voltage between the pointed end of a probe and adrawing target can suppress an anodic oxidation in in-plane directionsand promote the oxidation in the depth direction, thereby increasing theaspect ratio of the drawn linewidth. Applying a proper AC bias voltagein the sidewall lithography based on the same pattern transfer principlecan increase the aspect ratio of the transferred pattern.

FIG. 6 is a diagram illustrating an example of the AC bias voltage to beapplied between the transfer unit 2 and the transfer substrate 3.

The vertical axis represents the AC bias voltage and the horizontal axisrepresents a time. As illustrated in FIG. 6, the AC bias voltageincludes a positive transfer voltage V_(transfer) and a negative setvoltage V_(set) relative to the transfer substrate. According to theresults of experiments, applying an AC bias voltage instead of a directcurrent (DC) voltage and setting proper conditions successfullyfabricated a high-aspect-ratio pattern having a large thickness and asmall width of the pattern.

As a condition for the AC bias voltage, setting V_(transfer) to avoltage of 1 V or more and 40 V or less can provide voltage necessaryfor the oxidation and sufficient to keep the oxidation. Setting the ACbias voltage V_(set) to −V_(transfer) or more and smaller than 0 V cancancel the space charge that accumulates at the transferee side. Thiscancellation can prevent oxidation from proceeding in the horizontaldirection, thereby proceeding in the depth direction. Thus, the aspectratio of the transferred pattern can be improved.

Setting the frequency of the AC bias voltage to 0.1 Hz or more and 100Hz or less can fabricate a pattern with a high aspect ratio. A higherfrequency forms a meniscus having an unstable shape, which may lead toan unstable pattern transfer. Thus, setting the frequency to 0.1 Hz ormore and 100 Hz or less is preferred.

In transferring a pattern, an electrical potential is applied betweenthe transfer unit 2 and the transfer substrate 3 by the power source 5with the protruding structures 2 b of the transfer unit 2 and thepattern transfer surface of the transfer substrate 3 being in contactwith (or close to) each other. The sidewall electrodes 2 h cause thewater in the meniscus to ionize at contact regions (or close regions) onthe pattern transfer surface of the transfer substrate 3, therebyinducing anodic oxidation on the substrate. This anodic oxidationgenerates an oxidized pattern having a characteristic different from thecharacteristic of a region on which no anodic oxidation has occurred.

When, for example, the transfer substrate 3 is a silicon substrate,silicon atoms (Si) in an electron injection region ionize the water(H₂O) in a meniscus during injection of electrons, and oxygen (O₂) isprovided to the electron injection region. The oxygen oxidizes thesilicon atoms in the electron injection region and a silicon oxide(SiO_(x)) is formed thereon. As a result, a silicon oxide film havingthe same layout as the pattern formed by the sidewall electrodes 2 h isformed on the pattern transfer surface of the transfer substrate 3.Silicon and the silicon oxide have different etch resistance. In otherwords, etch resistance is one of the characteristics of the oxidegenerated by the anodic oxidation in this example. The characteristic tobe modified is not limited to etch resistance. In other words, thecharacteristic to be modified may be selected as appropriate dependingon the purpose. For example, chemical or physical characteristics(shape, for example) may be modified.

Described next is an example of a pattern transfer operation of thepattern transfer device 1 according to the first embodiment.

First, the transfer substrate 3 is placed on the humidity controller 4provided on the transfer substrate holder 7. The transfer unit 2 is heldby the transfer unit holder 6. The humidity controller 4 measures thehumidity and the temperature between the transfer unit 2 and thetransfer substrate 3 to calculate the dew point temperature. Thehumidity controller 4 changes the temperature of the transfer substrate3 based on the calculated dew point temperature to control the humidityon the transfer substrate 3 to 40% or more and 80% or less.

Subsequently, the transfer unit holder 6 moves in the Z direction tobring the protruding structures 2 b of the transfer unit 2 into contactwith the pattern transfer surface of the transfer substrate 3, and theprotruding structures 2 b are pressed against the surface. The state ofbeing in contact with the transfer substrate 3 includes a state in whichthe surfaces 2 d of the transfer unit 2 are directly in contact with thetransfer substrate 3 and includes a state in which the surfaces 2 d arein contact with the transfer substrate 3 via a water layer.

The power source 5 applies an AC bias voltage between the transfer unit2 and the transfer substrate 3. The AC bias voltage is set so that theaforementioned V_(transfer) is set to 1 V or higher and 40 V or lowerand V_(set) is set to higher than −V_(transfer) and lower than 0 V. Thefrequency of the AC bias voltage is set to 0.1 Hz or higher and 100 Hzor lower. With these settings, the pattern formed by the sidewallelectrodes 2 h is transferred to the transfer substrate 3.

After the pattern is transferred, the transfer unit holder 6 moves inthe Z direction to separate the transfer unit 2 from the transfersubstrate 3. If necessary, at least one of the transfer unit 2 and thetransfer substrate 3 may be moved to another region to be patterned onthe transfer substrate 3 so that the region is formed with the patternof an anodized film in the same manner. After a pattern is transferredonce, the pattern may be transferred a plurality of times on the samearea or transferred on the same area in a different orientation to forma layered transferred pattern.

FIGS. 7A to 7F illustrate SEM pictures of transferred patternstransferred by bringing a transfer unit having 30 nm width sidewallelectrodes into contact with a Si substrate under the humidity betweenthe transfer unit and the transfer substrate ranging from 40% to 80%.

An AC voltage of 17 V (with a duty cycle of 50% and a frequency of 1 Hz)was applied between the transfer substrate and the transfer unit for oneminute.

FIG. 7A illustrates a result of pattern transfer at 80% humidity, andFIG. 7B is an enlarged diagram of FIG. 7A. The linewidth of thetransferred pattern was as large as a few μm.

FIG. 7C illustrates a result of pattern transfer at 60% humidity, andFIG. 7D is an enlarged diagram of FIG. 7C. In this case, the linewidthof the transferred pattern was about 40 nm, which was close to 30 nmthat was the width of the sidewall electrodes of the transfer unit. FIG.7E illustrates a result of pattern transfer under the same conditions asdescribed above except at a reduced humidity of 40%. FIG. 7F is anenlarged diagram of FIG. 7E. According to the result of the patterntransfer, the linewidth of the transferred pattern was about 30 nm andthe transfer resolution was improved.

As described above, the pattern transfer device according to the firstembodiment controls the humidity between the transfer unit 2 and thetransfer substrate 3 to a certain humidity by using the humiditycontroller 4, and properly controls the voltage conditions of the powersource 5. This configuration can prevent degradation of resolution ofthe transferred pattern caused by a high humidity and can form a patternwith a high aspect ratio.

First Modification of First Embodiment

FIG. 8 is a diagram illustrating a pattern transfer device according toa first modification of the first embodiment.

The pattern transfer device according to the first modification of thefirst embodiment differs from the pattern transfer device according tothe first embodiment in that the humidity controller 4 is disposed onthe upper side of the transfer unit 2.

Specifically, the humidity controller 4 is disposed between the transferunit holder 6 and the transfer unit 2. The humidity controller 4 has,for example, openings 4 a that are in communication with at least one ofthe openings 6 a of the transfer unit holder 6. The transfer unit holder6 fixes the humidity controller 4 by suction from the openings 6 a. Sucha suction operation from the openings 6 a draws the transfer unit 2through the openings 4 a to hold the transfer unit 2. The transfer unit2 and the humidity controller 4 are not necessarily held by suction. Thetransfer unit 2 and the humidity controller 4 may be held by any methodthat can stably hold the transfer unit 2 and the humidity controller 4,such as using magnets, a sandwiching tool, or clips.

The humidity controller 4 changes the temperature of the transfer unit 2based on the humidity and the temperature on the transfer unit 2 tocontrol the humidity on the transfer unit 2 to a certain humidity.

Other configurations of the pattern transfer device according to thefirst modification of the first embodiment are the same as those of thepattern transfer device according to the first embodiment. With theseconfigurations, the pattern transfer device can prevent degradation of apattern resolution caused by an effect of humidity.

Second Modification of First Embodiment

FIG. 9 is a diagram illustrating a pattern transfer device according toa second modification of the first embodiment.

The pattern transfer device according to the second modification of thefirst embodiment differs from the pattern transfer device according tothe first embodiment in that it includes humidity controllers 4 one ofwhich is disposed at the upper side of the transfer unit 2 and the otherof which is disposed at the lower side of the transfer substrate 3.

Specifically, one humidity controller 4 is disposed between the transferunit holder 6 and the transfer unit 2. The other humidity controller 4is disposed between the transfer substrate 3 and the transfer substrateholder 7. The humidity controllers 4 are drawn, for example, from theopenings 6 a of the transfer unit holder 6 and from the openings 7 a ofthe transfer substrate holder 7 and are fixed thereto. The humiditycontrollers 4 each have openings 4 a that are in communication with atleast one of the openings 6 a or are in communication with at least oneof the openings 7 a. The transfer unit 2 and the transfer substrate 3are drawn from the openings 4 a and are held by the humidity controllers4.

The humidity controllers 4 may each include a power source of its own ormay be connected to a power source (not illustrated) included in thepattern transfer device.

Other configurations of the pattern transfer device according to thesecond modification of the first embodiment are the same as those of thepattern transfer device according to the first embodiment.

Providing the humidity controllers 4 to the transfer unit 2 and thetransfer substrate 3 can control the humidity more precisely, therebypreventing degradation of resolution of a pattern caused by an effect ofhumidity.

Second Embodiment

FIG. 10 is a diagram illustrating a pattern transfer device according toa second embodiment.

The pattern transfer device according to the second embodiment differsfrom the pattern transfer device according to the first embodiment inthat it includes a control chamber 8 instead of the humidity controller4.

The transfer unit 2, the transfer substrate 3, the transfer unit holder6, the transfer substrate holder 7, and the power source 5 are disposedinside the control chamber 8. The control chamber 8 may be, for example,a commercially available thermostatic chamber or an environment testchamber. The control chamber 8 controls the humidity in the chamber sothat the humidity between the transfer unit 2 and the transfer substrate3 is kept at a certain humidity. The power source 5 is not necessarilydisposed inside the control chamber 8. Wires from the transfer unit 2and the transfer substrate 3 may be extended to the outside of thecontrol chamber 8, at which the power source 5 may be connected to thewires. Other configurations of the pattern transfer device according tothe second embodiment are the same as those of the pattern transferdevice according to the first embodiment.

The pattern transfer device according to the second embodiment canstably control the humidity during pattern transfer by using the controlchamber 8 irrespective of the ambient temperature or humidity.

First Modification of Second Embodiment

FIG. 11 is a diagram illustrating a pattern transfer device according toa first modification of the second embodiment.

The pattern transfer device according to the first modification of thesecond embodiment differs from the pattern transfer device according tothe second embodiment in that it includes both the humidity controller 4and the control chamber 8.

The humidity controller 4 is disposed between the transfer substrate 3and the transfer substrate holder 7. The humidity controller 4 has, forexample, openings 4 a that are in communication with at least one of theopenings 7 a of the transfer substrate holder 7. The transfer substrateholder 7 fixes the humidity controller 4 by suction from the openings 7a. Such a suction operation from the openings 7 a draws the transfersubstrate 3 through the openings 4 a to hold the transfer substrate 3.

The pattern transfer device according to the first modification of thesecond embodiment does not necessarily completely control the humidityin the control chamber 8 to a stable humidity. The target humidity to becontrolled is the humidity between the transfer unit 2 and the transfersubstrate 3. Thus, the control chamber 8 may control the humidity tosome extent and the humidity controller 4 may control the humidity to acertain stable humidity.

As described above, using both the control chamber 8 and the humiditycontroller 4 can reduce the frequency of changing the temperature of thetransfer unit 2 or the transfer substrate 3 by a large degree, therebyreducing the time for controlling the humidity to a certain stablehumidity. The humidity in the control chamber 8 may be at the samehumidity level as that in typical clean rooms (50 to 60%). The humidityin the control chamber 8 can be changed as appropriate in accordancewith the target humidity between the transfer unit 2 and the transfersubstrate 3.

Second Modification of Second Embodiment

FIG. 12 is a diagram illustrating a pattern transfer device according toa second modification of the second embodiment.

The pattern transfer device according to the second modification of thesecond embodiment differs from the pattern transfer device according tothe first modification of the second embodiment in that the humiditycontroller 4 is disposed between the transfer unit 2 and the transferunit holder 6. Other configurations of the second modification of thesecond embodiment are the same as those in the first modification of thesecond embodiment.

Third Modification of Second Embodiment

FIG. 13 is a diagram illustrating a pattern transfer device according toa third modification of the second embodiment.

The pattern transfer device according to the third modification of thesecond embodiment differs from the pattern transfer device according tothe other modifications or embodiments in that it includes the controlchamber 8 and two humidity controllers 4 one of which is disposedbetween the transfer unit 2 and the transfer unit holder 6 and the otherof which is disposed between the transfer substrate 3 and the transfersubstrate holder 7. Other configurations of the third modification ofthe second embodiment are the same as those in the second embodiment.

As mentioned above, the control chamber 8 does not necessarily preciselycontrol the humidity to the target humidity. The control chamber 8 maycontrol the humidity to some extent and the humidity controllers 4 maycontrol the humidity to a certain stable humidity.

Using the control chamber 8 can reduce the frequency of changing thetemperature of the transfer unit 2 or the transfer substrate 3 by alarge degree. This configuration can reduce the time for controlling thehumidity to a certain stable humidity. In addition, providing twohumidity controllers 4 can precisely control the humidity between thetransfer unit 2 and the transfer substrate 3 and the humidity near thesurfaces thereof.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the inventions.

What is claimed is:
 1. A pattern transfer device comprising: asubstrate; a transfer unit having electrodes, the transfer unit beingconfigured to transfer a pattern corresponding to the electrodes with avoltage applied between the substrate and the electrodes; and acontroller configured to control humidity between the substrate and thetransfer unit.
 2. The pattern transfer device according to claim 1,wherein the transfer unit includes a plurality of protruding portionsfacing the substrate, and the electrodes are each disposed on a sidewallof the respective protruding portions.
 3. The pattern transfer deviceaccording to claim 1, wherein the voltage is an alternating current (AC)voltage.
 4. The pattern transfer device according to claim 3, wherein,when a maximum voltage of the AC voltage is represented by Vmax, theVmax is 1 V or higher and 40 V or lower.
 5. The pattern transfer deviceaccording to claim 4, wherein, when a minimum voltage of the AC voltageis represented by Vmin, the Vmin is higher than −Vmax and lower than 0V.
 6. The pattern transfer device according to claim 3, wherein the ACvoltage has a frequency of 0.1 Hz or higher and 100 Hz or lower.
 7. Thepattern transfer device according to claim 1, wherein the controllerkeeps the humidity between the substrate and the transfer unit at 30% ormore and 80% or less.
 8. The pattern transfer device according to claim1, wherein the controller is disposed at a lower side of the substrateor at an upper side of the transfer unit.
 9. The pattern transfer deviceaccording to claim 1 further comprising: a control chamber that containsthe substrate, the transfer unit, and the controller, wherein thecontrol chamber controls a humidity or a temperature inside the controlchamber.
 10. A pattern transfer device comprising: a substrate; atransfer unit having electrodes, the transfer unit being configured totransfer a pattern of the electrodes; and a control chamber containingthe substrate and the transfer unit, the control chamber beingconfigured to control humidity, wherein the pattern of the electrodes istransferred onto the substrate with a voltage applied between thesubstrate and the electrodes.
 11. A pattern transfer method employed ina pattern transfer device including a substrate, a transfer unit havingelectrodes, the transfer unit being configured to transfer a pattern ofthe electrodes, and a controller configured to control humidity betweenthe substrate and the transfer unit, the pattern transfer methodcomprising: bringing the electrodes of the transfer unit into contactwith the substrate; controlling the humidity between the substrate andthe transfer unit by the controller; and transferring the pattern of theelectrodes onto the substrate by applying a voltage between thesubstrate and the electrodes.
 12. The pattern transfer method accordingto claim 11, wherein the voltage is an AC voltage, and when a maximumvoltage of the AC voltage is represented by Vmax, the Vmax is 1 V orhigher and 40 V or lower.
 13. The pattern transfer method according toclaim 12, wherein the voltage is an AC voltage, and when a minimumvoltage of the AC voltage is represented by Vmin, the Vmin is higherthan −Vmax and lower than 0 V.
 14. The pattern transfer method accordingto claim 11, wherein the controlling includes keeping the humiditybetween the substrate and the transfer unit at 30% or more and 80% orless by the controller.